The electrodes of commercially available cochlear implant or auditory brainstem implant (ABI) systems may be used for acute electrical stimulation, obtaining important information about the electrodes itself and/or the implant system, or recording electrically evoked potentials (EEP), such as the compound action potential (CAP). The development of electrically evoked CAP responses enabled measurement of CAP responses via a cochlear implant. However, recordings of objective measurements of various other types of EEP via a cochlear or ABI implant are still problematic.
Evoked potentials include early, middle and late latency auditory responses, as described by Katz J., Handbook of Clinical Audiology, Williams & Wilkins 4th Edition, 1994, which is hereby incorporated herein by reference. By definition, the CAP is an alternating current response which is generated by the cochlear end of the VIIIth Cranial Nerve, and it represents the summed response of the synchronous firing of thousands of auditory nerve fibers, as described by: Ferraro et al., The Use of Electrocochleography in the Diagnosis, Assessment, and Monitoring of Endolymphatic Hydrops, Otolaryngologic Clinics of North America; 16:1, pp. 69-82, February, 1983; and Hall J. W., Handbook of Auditory Evoked Responses, Allyn and Bacon; Needham Heights, Mass., 1992, each of which is hereby incorporated herein by reference. The auditory brainstem response (ABR) is an electrical signal evoked from the brainstem of a human or other mammal by the presentation of a specific signal (Katz, 1994). The first recording of an ABR potential in man was performed by Jewett D. L. et al., Human Auditory Evoked Potentials: Possible Brain Stem Ccomponents Detected on the Scalp, Science 1970; 167: p. 1517-8, which is hereby incorporated herein by reference. The relationship of specific wave components of the ABR to the components of the auditory pathway can be represented as follows: wave I: Cochlear Action Potential (CAP), distal CNVIII; wave II: proximal CNVIII; wave III: Cochlear Nuclei; wave IV: Superior Olivary Complex; and wave V: Lateral Lemniscus. The definition of peaks is described in Jewett D. L. et al., Auditory-evoked Far Fields Averaged from the Scalp of Humans, Brain. 1971; 94(4): p. 681-96, which is hereby incorporated herein by reference.
Electrically evoked Auditory Brainstem Responses (eABR) may be obtained by recording a series of potentials with, in part, one or more scalp electrodes. The response typically occurs within 10 msec after onset of a pulsatile stimulus. The pulsatile stimulus may be provided, for example, by an electrode associated with a cochlear implant or ABI.
In many instances, electrically evoked Auditory Brainstem Responses (eABR) can provide information useful for implants. For example, eABR can provide important information regarding hearing, and using a specific stimuli may provide electrode specific hearing information of a subject. While the CAP measurement can obtain information about nerve fibres within the cochlea, eABR has the ability to check auditory pathway, i.e. assessing the functions of the inner ear, VIII cranial nerves, and various brain functions of the lower part of the auditory system.
For eABR via an ABI, the electrode array is placed directly on the cochlear nucleus, Therefore, the eABR recordings cannot include recordings of waves I, II and partially wave III, and occurs 1-2 ms earlier than it does with a cochlear implant. Since stimulating artifacts are present substantially immediately after the presented stimuli and at the beginning of the recordings, analysis of eABR via ABI is typically more difficult than it is for eABR via a cochlear implant. In the fitting process, for ABI subjects who never heard or have only very little experiences with the hearing (for example, children), eABR becomes a very important objective measurement. Compared to cochlear implant patients, eABR may be of higher importance for ABI patients as some objective measurements often used in the fitting process in cochlear implant patients, may not be elicitable, i.e. electrically evoked stapedial reflex measurement (eSR).
Particular uses of eABR are listed below.                eABR may serve as an aid for the intra-operative or post-operative confirmation of electrode placement, and functionality of the implant (see: Behr R. et al., The High Rate CIS Auditory Brainstem Implant for Restoration of Hearing in NF-2 Patients, Skull. Base 17(2), 2007, p. 91-107; and Bahmer A. et al., Recording of Electrically Evoked Auditory Brainstem Responses (E-ABR) with an Integrated Stimulus Generator in Matlab, Journal Neuroscience Methods 173(2), 2008, p. 306-314, each of which is hereby incorporated herein by reference. eABR has become a standard measurement for use in judging the proper placement of the electrode paddle on a cochlear nucleus.        eABR may serve an aid for diagnostic assessment of a patient (see Gibson et al., The Use of Intra-operative Electrical Auditory Brainstem Responses to Predict the Speech Perception Outcome after Cochlear Implantation, Cochlear. Implants Int., 10 Suppl 1 2009, p. 53-57, which is hereby incorporated herein by reference). In particular, eABR can be a tool for the assessment and monitoring of audiologic, otologic and neurologic disorders (i.e. acoustic tumor monitoring).        eABR may be used as an aid for the post-operative programming of a hearing implantable device, especially in difficult-to-fit patients such as children (see: Brown C. J. et al., The relationship between EAP and EABR thresholds and levels used to program the nucleus 24 speech processor: data from adults, Ear Hear. 21(2), 2000, and McMahon et al., 2008, p. 151-163; and McMahon C. M. et al., Frequency-specific Electrocochleography Indicates that Presynaptic and Postsynaptic Mechanisms of Auditory Neuropathy Exist, Ear Hear. 29(3), 2008, p. 151-163, each of which is hereby incorporated herein by reference).        eABR may provide additional information on psychoacoustic thresholds for each intracochlear or electrode (see Brown et al., 2000)        eABR may be used as an aid to provide quantitative information on auditory pathway (See: Polak M. et al., Evaluation of Hearing and Auditory Nerve Function by Combining ABR, DPOAE and eABR Tests into a Single Recording Session, J. Neurosci. Methods 134(2), 2004, p. 141-149; and Gibson et al., 2009).        
Obtaining eABRs can be cumbersome. An external system for recording is typically required, which then has to interface/synchronize with the stimulation system. Various recording electrodes need to be positioned on the patient, the location of which may be susceptible to movement by the patient.
Furthermore, commercially available recording systems often record stimuli artifacts together with the physiological response. These artifacts may be much higher than the physiological response (artifacts are up to several decade times higher than a physiological response). Thus, it is often very difficult to judge if the physiological response is present. Sometimes, the artifacts are confused with the physiological response, and thus the final interpretation of the results may lead to an incorrect interpretation. For intraoperative measurement, when relying only on the eABR response, inappropriate judgement may have a very dramatic influence on postoperative performance with the implant system. For eABR recordings, only an alternating artifact cancellation method is being used commercially (for example, see Polak et al., 2004). However, this method is often not satisfactory in cancelling out the stimuli artifacts.